The present assignee has provided several systems for either lowering or raising a window covering, or for moving the slats of a window covering between open and closed positions, under control of a hand-held remote or other control device. These systems include a motor that is coupled through gears to the window covering activation mechanism. When the motor is energized in response to a user command signal, the activation mechanism moves the window covering. Such assemblies are disclosed in U.S. Pat. No. 6,433,498, incorporated herein by reference.
The present assignee has also provided systems for determining the position of the window coverings based on counting motor pulses. By knowing the position of the window coverings, features such as automatic repositioning the window covering to a preset position can be provided.
As recognized herein, brush-based position encoders for outputting the positions of rotating shafts have been provided, and advantageously tend to be inexpensive and reliable. In brush-based systems, brushes are provided that ride on tracks each of which describes a portion of a circle and each of which is staggered relative to the other two, i.e., the three tracks have different radii than each other. Either the brushes rotate with the shaft and the tracks are stationary, or the tracks rotate with the shaft and the brushes are stationary. In either case, to provide a quadrature signal output, three tracks and three brushes are used, one brush per track.
As further recognized herein, such brush-based systems require sufficient space to accommodate the three tracks, making them difficult to fit into small systems. Also, each brush must be lined up with each track, to ensure it rides on its track and only its track. The positioning of the brushes is thus critical, requiring tighter tolerances between components and, thus, higher manufacturing costs. Having made the critical observation that a brush-based quadrature position encoder is needed that can fit into small systems and/or that permits the use of looser tolerances for positioning brushes than is currently possible, the present invention has been provided.